Explicit incorporation of deformation twins into crystal plasticity finite element models (original) (raw)
Related papers
Incorporation of deformation twinning in crystal plasticity models
Journal of the Mechanics and Physics of Solids, 1998
A new constitutive framework, together with an efficient time-integration scheme, is presented for incorporating the crystallography of deformation twinning in polycrystal plasticity models. Previous approaches to this problem have required generation of new crystal orientations to reflect the orientations in the twinned regions or implementation of "volume fraction transfer" schemes, both of which require an update of the crystal orientations at the end of each time step in the simulation of the deformation process. In the present formulation, all calculations are performed in a relaxed configuration in which the lattice orientation of the twinned and the untwinned regions are pre-defined based on the initial lattice orientation of the crystal. The validity of the proposed constitutive framework and the time-integration procedures has been demonstrated through comparisons of predicted rolling textures in low stacking fault energy fee metals and in hcp metals with the corresponding predictions from the earlier approaches as well as through qualitative comparisons with the measurements reported previously. I('>
Acta Materialia, 2012
Different approaches to the modeling of twinning are examined within the framework of a crystal plasticity finite-element code. The model predictions are compared with in situ neutron diffraction experiments previously carried out on zirconium and magnesium alloys. The experiments are used to evaluate different model assumptions regarding the stress state inside newly formed twins at inception, as well as different assumptions concerning the interaction between twin and parent grain during subsequent twin growth. In particular the relaxation in some grain orientations that is experimentally observed, and is associated with twin-induced stress relief, can be captured by the model under appropriate assumptions.
Role of Deformation Twinning on Strain Hardening in Cubic and Hexagonal Polycrystalline Metals
Advanced Engineering Materials, 2003
Besides crystallographic slip, deformation twinning is the most prevalent mechanism of plastic deformation in many materials. Novel experiments were conducted in cubic and hexagonal metals to elucidate the effect of deformation twins on subsequent mechanical response. Orientation Imaging Microscopy TM (OIM) and indentation techniques were employed in conjunction with conventional mechanical testing and optical microscopy to obtain new insights. Here, we show direct and clear evidence for hardening of the material by deformation twinning due to both a reduction of the effective slip length (Hall±Petch effect) and an increase in hardness of the twinned regions (Basinski mechanism), as well as softening due to lattice reorientation of the twinned regions. These results appear to explain the seemingly contradictory results that have been reported previously on the strengthening effects of twins.
Journal of the Mechanics and Physics of Solids, 2019
Calibrating and verifying crystal plasticity material models is a significant challenge, particularly for materials with a number of potential slip and twin systems. Here we use digital image correlation on coarse-grained α-uranium during tensile testing in conjunction with crystal plasticity finite element simulations. This approach allows us to determine the critical resolved shear stress, and hardening rate of the different slip and twin systems. The constitutive model is based on dislocation densities as state variables and the simulated geometry is constructed from electron backscatter diffraction images that provide shape, size and orientation of the grains, allowing a direct comparison between virtual and real experiments. An optimisation algorithm is used to find the model parameters that reproduce the evolution of the average strain in each grain as the load is increased. A tensile bar, containing four grains aligned with the load direction, is used to calibrate the model with eight unknown parameters. The approach is then independently validated by simulating the strain distribution in a second tensile bar. Different mechanisms for the hardening of the twin systems are evaluated. The latent hardening of the most active twin system turns out to be determined by coplanar twins and slip. The hardening rate of the most active slip system is lower than in fine-grained α-uranium. The method developed in the present research can be applied to identify the critical resolved shear stress and hardening parameters of other coarse-grained materials.
International Journal of Plasticity, 2019
This work adapts a recently developed multi-level constitutive model for polycrystalline metals that deform by a combination of elasticity, crystallographic slip, and deformation twinning to interpret the deformation behavior of alloy WE43 as a function of strain rate. The model involves a two-level homogenization scheme. First, to relate the grain level to the level of a polycrystalline aggregate, a Taylor-type model is used. Second, to relate the aggregate level response at each finite element (FE) integration point to the macro-level, an implicit FE approach is employed. The model features a dislocation-based hardening law governing the activation stress at the slip and twin system level, taking into account the effects of temperature and strain rate through thermally-activated recovery, dislocation debris formation, and slip-twin interactions. The twinning model employs a composite grain approach for multiple twin variants and considers double twinning. The alloy is tested in simple compression and tension at a quasistatic deformation rate and in compression under high strain rates at room temperature. Microstructure evolution of the alloy is characterized using electron backscattered diffraction and neutron diffraction. Taking the measured initial texture as inputs, it is shown that the model successfully captures mechanical responses, twinning, and texture evolution using a single set of hardening parameters, which are associated with the thermally activated rate law for dislocation density across strain rates. The model internally adjusts relative amounts of active deformation modes based on evolution of slip and twin resistances during the imposed loadings to predict the deformation characteristics. We observe that WE43 exhibits much higher strain-hardening rates under high strain rate deformation than under quasi-static deformation. The observation is rationalized as primarily originating from the pronounced activation of twins and especially contraction and double twins during high strain rate deformation. These twins are effective in strain hardening of the alloy through the texture and barrier hardening effects.
Modeling of twinning-induced plasticity using crystal plasticity and thermodynamic framework
Acta Mechanica, 2019
In many applications of steels, especially in aerospace and petroleum industry, large deformation is required in order to achieve complex shape and geometry of finished products. In these, advanced highstrength steels play a vital role by attaining favorable amalgamation of high strength and ductility. Among all second-generation steels, twinning-induced plasticity contains a significant percentage of austenite phase, shows outstanding tensile strength and ductility. The primary cause of having these outstanding properties is found to be stress-assisted austenite to martensite phase transformation, commonly described as twinning. In this paper, a micromechanical model is developed in the thermomechanical framework to investigate elasticplastic deformation of twinning-induced plasticity steel. It is assumed that plastic deformation is caused due to slip and mechanical twinning under given loading conditions. Firstly, a micromechanical constitutive model, considering slip and mechanical twinning as sources of permanent deformation, is developed by kinematic decomposition of an austenite crystal into intermediate configurations. Secondly, a thermodynamic framework is used to formulate driving potentials for slip and twinning mechanisms. Thirdly, the developed model is numerically implemented into finite element software ABAQUS by a user-defined material subroutine. Finally, the deformation behavior of single and polycrystalline austenite are predicted by numerical simulations in tension compression, and simple shear loading conditions. It is found that in tension twin deformation plays a dominant role, while the reverse is observed in compression. In simple shear, on an activation of twin mode, slip systems encounter higher slip resistance due to slip-slip and slip-twin interactions.
A crystal plasticity model for twinning-and transformation-induced plasticity
A dislocation density-based crystal plasticity model incorporating both transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) is presented. The approach is a physically-based model which reflects microstructure investigations of ε-martensite, twins and dislocation structures in high manganese steels. Validation of the model was conducted using experimental data for a TRIP/TWIP Fe-22Mn-0.6C steel. The model is able to predict, based on the difference in the stacking fault energies, the activation of TRIP and/or TWIP deformation mechanisms at different temperatures.
2014
Nanotwinned (nt) metals are an important subset of nanostructured materials because they exhibit impressive strength and ductility. Several recent investigations on nt face-centeredcubic (FCC) metals indicate that their macroscopic responses emerge from complex microscopic mechanisms that are dominated by dislocation-TB interactions. Under applied stimulus, nt microstructures evolve through migration of twin boundaries (TBs) that may have implications on the material strength and stability. This work focuses on modeling TB migration within finite element framework in an explicit manner and studying its effects on the micromechanics of twinned FCC metals under quasi-static loading conditions. The theoretical setting is developed using three-dimensional single crystal plasticity as a basis wherein the plastic slip on the f111g〈110〉 slip systems in an FCC crystal structure is modeled as visco-plastic behavior. Owing to their governing role, twins are modeled as discrete lamellas with full crystallographic anisotropy. To model TB migration, an additional viscoplastic slip-law for twinning partial systems ðf111g〈112〉Þ based on the nucleation and motion of twin partial dislocations is introduced. This size-dependent constitutive law is presumed to prevail in the vicinity of the TB and naturally facilitates TB migration when combined with a twinning condition that is based on the accrual of the necessary shear strain. The constitutive development is implemented within a finite element framework through a User Material (UMAT) facility within ABAQUS=STANDARD s . Detailed micromechanics simulations on model microstructures involving single-grained and polycrystalline topologies are presented.
Materials Science and Engineering: A, 2009
Depleted uranium is of current programmatic interest at Los Alamos National Lab due to its high density and nuclear applications. At room temperature, depleted uranium displays an orthorhombic crystal structure with highly anisotropic mechanical and thermal properties. For instance, the coefficient of thermal expansion is roughly 20 × 10 −6 • C −1 in the a and c directions, but near zero or slightly negative in the b direction. The innate anisotropy combined with thermo-mechanical processing during manufacture results in spatially varying residual stresses and crystallographic texture, which can cause distortion, and failure in completed parts, effectively wasting resources. This paper focuses on the development of residual stresses and textures during deformation at room and elevated temperatures with an eye on the future development of computational polycrystalline plasticity models based on the known micro-mechanical deformation mechanisms of the material.
Acta Materialia, 2023
Twin, dislocation, and grain boundary interaction in hexagonal materials, such as Mg, Ti, and Zr, has critical influence on the materials' mechanical properties. The development of a microstructure-sensitive constitutive model for these deformation mechanisms is the key to the design of high-strength and ductile alloys. In this work, we have developed a mechanical formulation within the finite strain framework for modeling dislocation slip-and deformation twinning-induced plasticity. A dislocation density-based crystal plasticity model was employed to describe the dislocation activities, and the stress and strain distributions. The model was coupled with a multi-phase-field model to predict twin formation and twin-twin interactions. The coupled model was then employed to study twin, dislocation, and grain boundary interactions in Mg single-and polycrystals during monotonic and cyclic deformation. The results show that twin-twin interactions can enhance the strength by impeding twin propagation and growth. The role of dislocation accommodation on twin-twin interactions was twofold. Dislocation slip diminished twin-twin hardening by relieving the development of back-stresses, while it effectively relaxed the stress concentration near twin-twin intersections and thus may alleviate crack nucleation. The plastic anisotropy in each grain and the constraints imposed by the local boundary conditions resulted in stress variations among grains. This stress heterogeneity was responsible for the observed anomalous twinning behaviour. That is, low Schmid factor twins were activated to relax local stresses and accommodate the strain incompatibility, whereas the absence of high Schmid factor twins was associated with slip band-induced stress relaxation.